The astronauts released a 1,700-pound ammonia coolant tank in the shuttle Discovery’s cargo bay so it could be moved to the space station and installed a rate gyro assembly, a device that helps determine the lab’s orientation in space. They also carried out a variety of get-ahead tasks to save time for future spacewalkers.

This was the 141st spacewalk devoted to station assembly and maintenance since construction began in 1998, the fifth so far this year and the first of three planned by Discovery’s crew. Total station EVA time now stands at 879 hours and 43 minutes.